The admittance of test MIS structures based on nBn systems from Hg1 – xCdxTe grown by molecular beam epitaxy is investigated. Composition x in the absorbing and contact layers is 0.29; in the barrier layer, it is 0.60. An equivalent circuit of an MIS-structure based on an nBn system is proposed and the nominal values of the elements of this circuit are found under various conditions. Comparison of the temperature dependence of the barrier resistance with the Rule07 model indicates the possibility of creating efficient nBn detectors based on HgCdTe grown by molecular beam epitaxy for the 3- to 5-μm spectral range.